1. Field of the Invention
The disclosed invention relates generally to an electronic circuit allowing detection of a cable and that cable's type and a method of detecting a cable using the electronic circuit, and in particular, to an electronic circuit which allows detection of a video cable and the determination of whether the cable is an analog or digital video cable.
2. Description of the Related Art
Computers are becoming increasingly important in nearly every aspect of daily life. They may be found in the home, in the office, and in nearly every aspect of daily life. Most computers utilize a display apparatus with which to visually communicate information to a user. The display apparatus may be a liquid crystal display (“LCD”) an organic light emitting diode (“OLED”) display, a cathode ray tube (“CRT”) display, or any of several other well known displays.
The display apparatus is connected to the computer, typically using a video cable having one end connected to a connector on the computer an opposite end connected to another connector located on the display apparatus.
Computers have reduced in size while retaining or adding new capabilities. This has put space constraints on components of the computer. Various components have shrunk to meet smaller size requirements associated with smaller, more complex computers, including the components used to communicate with the display apparatus. The components used to communicate with the display apparatus are known as video units. Because of the reduced size requirements, most video units include only a single connector with which to connect to a display apparatus via a video cable.
The connectors on the video unit and the display apparatus typically consist of a collection of terminals as female conductor connectors, and the ends of the video cable typically consist of a corresponding number of pins as male conductor connectors which may be inserted into the terminals, making a male/female connection on both the video unit and the display apparatus. The video unit sends various components of video signals through individual holes of the female conductor connector, along the video cable, to the display apparatus.
As the uses for computers have increased, so has the amount of information which they are able to communicate. It is not uncommon to have a single computer connected to multiple display apparatuses. These multiple displays may increase the total display area available for displaying information thereon. However, due to the abovementioned space constraints, the video units typically do not have the required space to support multiple connectors with which to connect with multiple display apparatus. Therefore, the single connector on the video unit must serve as the connection to multiple display apparatus. It typically does so through the use of a split, or Y, connector video cable. The end of the Y-connector having a single branch connects to the single connector on the video unit and each of the branches on the opposite side may connect to a display apparatus.
In addition to connecting to multiple displays, the computer may be able to communicate with the display apparatus using various forms of video signals. The computer may send digital video displays to the display apparatus and the computer may send analog signals to the display apparatus. The display apparatus may be capable of receiving both digital and analog signals; however, the connector video cable is incapable of transmitting both digital and analog signals. The connector video cable typically transmits only digital or only analog signals. As mentioned above due to space requirements, the video unit of the computer typically only has one connector with which to output either type of signal.
The video cable used with a digital signal is not able to transmit an analog signal, and a video cable used with an analog signal is not able to transmit a digital signal. A user wishing to connect the computer with an analog display would use an analog video cable to connect the computer's video unit to the display apparatus; and similarly, a user wishing to connect the computer with a digital display would use a digital video cable. In addition, the user would have to set a switch position or insert a jumper on the computer, or the video unit itself, to communicate to the video unit which type of cable is connected. This requires an extra setup step for the user and presents a situation where the user may accidentally set the switch/jumper improperly. There is a need to simplify the setup procedure associated with selecting the appropriate signal to send to the attached video cable.
Various techniques have been developed to automatically differentiate which cable type is connected to a system. One method includes using a capacitor/resistor network formed by the cable and passive components on the computer. In this method, a special signal, such as the PDIAG signal, which is already defined on the off-the-shelf cable, is routed through a hole in the system to a unique pin on the cable. The unique pin is connected on one cable in such a way as to differentiate it from another cable by grounding the PDIAG signal but without interfering with previously defined usages of this signal. On another cable, the signal is routed uninterrupted from one end of the cable to the other. This allows the type of cable to be detected based on the state of the PDIAG signal on the unique pin. One substantial drawback to this method is that it requires the use of a special pin on the connector and cable just to differentiate between the two cable types. Furthermore, off-the-shelf video cables do not provide a pin for such a special signal. The use of non-standard cables and connectors increases the costs associated with the manufacture of displays and computers. Additionally, computer video units equipped with the non-standard connector are not compatible with standard display apparatus and therefore are less attractive to users.
Similarly, another method is to include a special terminal in the video unit connector and on the display apparatus connector which corresponds to a unique pin on the video cable. The terminal on the video unit connector serves to detect and identify information about the cable to the video unit. The pin's only purpose is to determine whether an analog or digital connector is attached thereto. Again, this method must use non-standard connector pinouts, which increases costs and is less attractive to users.
Another method of automatically differentiating which cable type is connected to the video unit is to embed mechanical switches into the connector of the video unit. These switches, often called microswitches, are physically triggered by the insertion of the video cable into the video unit. This method requires the addition of switches to the video unit, which may increase its size beyond practical limitations. The switches are prone to deterioration with time since they work on a mechanical basis and contain several small, precision made parts. Because of those miniature precision parts, the switches also increase the cost of the video unit on which they are located.
Accordingly, a method and apparatus for simplifying the setup procedure associated with selecting the appropriate signal to send to the attached video cable without using microswitches or non-standard connectors is desired.